全文获取类型
收费全文 | 496篇 |
免费 | 27篇 |
专业分类
化学 | 391篇 |
晶体学 | 4篇 |
力学 | 6篇 |
数学 | 45篇 |
物理学 | 77篇 |
出版年
2023年 | 8篇 |
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 17篇 |
2019年 | 11篇 |
2018年 | 11篇 |
2017年 | 10篇 |
2016年 | 13篇 |
2015年 | 19篇 |
2014年 | 22篇 |
2013年 | 36篇 |
2012年 | 31篇 |
2011年 | 49篇 |
2010年 | 18篇 |
2009年 | 31篇 |
2008年 | 22篇 |
2007年 | 20篇 |
2006年 | 26篇 |
2005年 | 30篇 |
2004年 | 22篇 |
2003年 | 29篇 |
2002年 | 23篇 |
2001年 | 9篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1996年 | 4篇 |
1994年 | 2篇 |
1993年 | 6篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有523条查询结果,搜索用时 15 毫秒
501.
A problem of goodness-of-fit test for ergodic diffusion processes is presented. In the null hypothesis the drift of the diffusion is supposed to be in a parametric form with unknown shift parameter. Two Cramer–von Mises type test statistics are studied. The first test uses the local time estimator of the invariant density, the second one uses the empirical distribution function. The unknown parameter is estimated via the maximum likelihood estimator. It is shown that the limit distribution of the two test statistics does not depend on the unknown parameter, thus both the tests are asymptotically parameter free. Some considerations on the consistency of the proposed tests and some simulation studies are also given. 相似文献
502.
Dr. Mikhail S. Baranov Dr. Kyril M. Solntsev Nadezhda S. Baleeva Dr. Alexander S. Mishin Prof. Sergey A. Lukyanov Dr. Konstantin A. Lukyanov Dr. Ilia V. Yampolsky 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(41):13234-13241
A novel class of fluorescent dyes based on conformationally locked GFP chromophore is reported. These dyes are characterized by red‐shifted spectra, high fluorescence quantum yields and pH‐independence in physiological pH range. The intra‐ and intermolecular mechanisms of radiationless deactivation of ABDI‐BF2 fluorophore by selective structural locking of various conformational degrees of freedom were studied. A unique combination of solvatochromic and lipophilic properties together with “infinite” photostability (due to a dynamic exchange between free and bound dye) makes some of the novel dyes promising bioinspired tools for labeling cellular membranes, lipid drops and other organelles. 相似文献
503.
Choi SH Guzei IA Spencer LC Gellman SH 《Journal of the American Chemical Society》2008,130(20):6544-6550
Oligomers that contain both alpha- and beta-amino acid residues in a 1:1 alternating pattern have recently been shown by several groups to adopt helical secondary structures in solution. The beta-residue substitution pattern has a profound effect on the type of helix formed and the stability of the helical conformation. On the basis of two-dimensional NMR data, we have previously proposed that beta-residues with a five-membered ring constraint promote two different types of alpha/beta-peptide helix. The "11-helix" contains i, i+3 CO...H-N hydrogen bonds between backbone amide groups; these hydrogen bonds occur in 11-atom rings. The alpha/beta-peptide "14/15-helix" contains i, i+4 CO...H-N hydrogen bonds, which occur in alternating 14- and 15-atom rings. Here we provide crystallographic data for 14 alpha/beta-peptides that form the 11-helix and/or the 14/15-helix. These results were obtained for a series of oligomers containing beta-residues derived from ( S,S)- trans-2-aminocyclopentanecarboxylic acid (ACPC) and alpha-residues derived from alpha-aminoisobutyric acid (Aib) or l-alanine (Ala). The crystallized alpha/beta-peptides range in length from 4 to 10 residues. Nine of the alpha/beta-peptides display the 11-helix in the solid state, three display the 14/15-helix, and two display conformations that contain both i, i+3 and i, i+4 CO...H-N hydrogen bonds, but not bifurcated hydrogen bonds. Only 3 of the 14 crystal structures presented here have been previously described. These results suggest that longer alpha/beta-peptides prefer the 14/15-helix over the 11-helix, a conclusion that is consistent with previously reported NMR data obtained in solution. 相似文献
504.
Ilia I. Sadykov Dr. Vitaly L. Sushkevich Dr. Frank Krumeich Dr. Rob Jeremiah G. Nuguid Prof. Dr. Jeroen A. van Bokhoven Dr. Maarten Nachtegaal Dr. Olga V. Safonova 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(1):e202214032
Operando X-ray absorption spectroscopy identified that the concentration of Fe2+ species in the working state-of-the-art Pt−FeOx catalysts quantitatively correlates to their preferential carbon monoxide oxidation steady-state reaction rate at ambient temperature. Deactivation of such catalysts with time on stream originates from irreversible oxidation of active Fe2+ sites. The active Fe2+ species are presumably Fe+2O−2 clusters in contact with platinum nanoparticles; they coexist with spectator trivalent oxidic iron (Fe3+) and metallic iron (Fe0) partially alloyed with platinum. The concentration of active sites and, therefore, the catalyst activity strongly depends on the pretreatment conditions. Fe2+ is the resting state of the active sites in the preferential carbon monoxide oxidation cycle. 相似文献
505.
506.
Min Ji Kim Diana J. Wang Karina Targos Uriel A. Garcia Alison F. Harris Ilia A. Guzei Zachary K. Wickens 《Angewandte Chemie (International ed. in English)》2023,62(21):e202303032
Cyclopropanes are desirable structural motifs with valuable applications in drug discovery and beyond. Established alkene cyclopropanation methods give rise to cyclopropanes with a limited array of substituents, are difficult to scale, or both. Herein, we disclose a new cyclopropane synthesis through the formal coupling of abundant carbon pronucleophiles and unactivated alkenes. This strategy exploits dicationic adducts derived from electrolysis of thianthrene in the presence of alkene substrates. We find that these dielectrophiles undergo cyclopropanation with methylene pronucleophiles via alkenyl thianthrenium intermediates. This protocol is scalable, proceeds with high diastereoselectivity, and tolerates diverse functional groups on both the alkene and pronucleophile coupling partners. To validate the utility of this new procedure, we prepared an array of substituted analogs of an established cyclopropane that is en route to multiple pharmaceuticals. 相似文献
507.
We investigate sums \(J(\vec {x})\) and \(L(\vec {x})\) of pairs of normalized Saalschützian \({}_4F_3(1)\) hypergeometric series, and develop a theory of relations among these J and L functions. The function \(L(\vec {x})\) has been studied extensively in the literature and has been shown to satisfy a number of two-term and three-term relations with respect to the variable \(\vec {x}\). More recent works have framed these relations in terms of Coxeter group actions on \(\vec {x}\) and have developed a similar theory of two-term and three-term relations for \(J(\vec {x})\). In this article, we derive “mixed” three-term relations, wherein any one of the L (respectively, J) functions arising in the above context may be expressed as a linear combination of two of the above J (respectively, L) functions. We show that, under the appropriate Coxeter group action, the resulting set of three-term relations (mixed and otherwise) among J and L functions partitions into eighteen orbits. We provide an explicit example of a relation from each orbit. We further classify the eighteen orbits into five types, with each type uniquely determined by the distances (under a certain natural metric) between the J and L functions in the relation. We show that the type of a relation dictates the complexity (in terms of both number of summands and number of factors in each summand) of the coefficients of the J and L functions therein. 相似文献
508.
Dymon J Wibby R Kleingardner J Tanski JM Guzei IA Holbrey JD Larsen AS 《Dalton transactions (Cambridge, England : 2003)》2008,(22):2999-3006
A range of new alkylpyridinium and imidazolium carborane salts with [nido-C(2)B(9)H(12)](-), [closo-CB(11)H(12)](-), and [RC(2)B(11)H(11)](-) (R = methyl or butyl) anions have been prepared and characterized by physical and thermal methods, including the solid state structures of five of the salts determined by single crystal X-ray diffraction. The tendency of the salts to form low-melting ionic liquids has been assessed; all the salts studied with [nido-C(2)B(9)H(12)](-) anions melted below 100 degrees C and, significantly, have melting points that are 25-85 degrees C lower than those of the corresponding [closo-CB(11)H(12)](-) analogs, demonstrating that a wider range of boron-rich ionic liquid materials can be readily accessed. 相似文献
509.
Ilia Krasikov 《Constructive Approximation》2008,28(2):113-125
T. Erdelyi, A.P. Magnus and P. Nevai conjectured that for
the orthonormal Jacobi polynomials
satisfy the inequality
[Erdelyi et al., Generalized Jacobi weights, Christoffel functions, and Jacobi polynomials. SIAM J. Math. Anal., 25 (1994),
602-614.]. Here we will confirm this conjecture in the ultraspherical case
even in a stronger form by giving very explicit upper bounds. We also show that
for a certain choice of
such that the interval
contains all the zeros of
Slightly weaker bounds are given for polynomials of odd degree. 相似文献
510.
An efficient asymmetric synthesis of the 22nd amino acid L-pyrrolysine has been accomplished. The key stereogenic centers were installed by an asymmetric conjugate addition reaction. A Staudinger/aza-Wittig cyclization was used to form the acid-sensitive pyrroline ring. Pyrrolysine was synthesized in 13 steps in 20% overall yield. 相似文献